With ongoing miniaturization, conventional silicon microelectronics will reach its limit. Disruptive short-channel effects are becoming an ever more important factor with ongoing miniaturization in a field-effect transistor, restricting the conductivity of the field-effect transistor. In addition to the problems which arise in an individual component, a further difficulty in a memory arrangement is a limited scaleability of the storage medium, for example the capacitance in a DRAM (dynamic random access memory) cannot be scaled to any desired degree.
The use of carbon nanotubes is under discussion as a possible successor technology to silicon microelectronics. Basic principles of carbon nanotubes are described, for example, in Harris, P J F (1999) “Carbon Nanotubes and Related Structures—New Materials for the Twenty-first Century”, Cambridge University Press, Cambridge, pp. 1 to 15, 111 to 155. It is known that carbon nanotubes (depending on the tube parameters) have an electrical conductivity ranging from semiconducting to metallic.
On account of their electrical properties, carbon nanotubes are being studied not only as a possible alternative to conventional active elements, such as field-effect transistors, diodes, etc., but also, on account of their high current-carrying capacity and small dimensions in the range of nanometer, as a replacement for conventional metallization material (aluminium, copper, etc.). Since the coupling of electrical switching elements in a circuit requires the production not only of simple point-to-point interconnects but also of branched electrical lines, there is a need for it to be possible to branch current paths using carbon nanotubes.
It is known from Li, J. Papadopoulos, C Xu, J (1999) “Nanoelectronics: Growing Y-junction carbon nanotubes”, Nature 402:253–254 to produce a Y-shaped junction of carbon nanotubes by forming a spot of catalyst material in an end section of a Y-shaped channel in an aluminium oxide template (Al2O3). Then, in accordance with Li et al., a carbon nanotube with a Y-shaped junction is formed in the channel starting from the spot of catalyst material by means of pyrolysis of acetylene.
However, the process which is known from Li et al. is restricted to the formation of branched carbon nanotubes inside a template.
At some locations, branched carbon nanotubes may randomly result during the synthesis of carbon nanotubes, for example using a CVD process (chemical vapour deposition). However, this process cannot be used to control the spatially defined formation of branched carbon nanotubes.
It is known from Cheung, C L, Kurtz, A, Park, H, Lieber, C M (2002) “Diameter-Controlled Synthesis of Carbon Nanotubes”, JPhysChemB 106:2429–2433 to deposit iron clusters of predeterminable size on a substrate and to grow on carbon nanotubes using a CVD process starting from the iron clusters which have a catalytic action for the growth of carbon nanotubes. The diameter of the carbon nanotubes can be set by predetermining the diameter of the clusters.
Murray, C B, Sun, S, Doyle, H, Betley, T “Monodispersive 3d Transition-Metal (Co, Ni, Fe) Nanoparticles and Their Assembly into Nanoparticle Superlattices”, MRS Bulletin, December 2001, discloses a process by which metal clusters can be produced from 3d transition metals.
Cao, A, Zhang, X, Xu, C, Liang, J, Wu, D, Wei, B (2000) “Carbon nanotube dendrites: Availability and their growth model”, Materials Research Bulletin 36:2519–2523, discloses a growth model for dendrites of carbon nanotubes.
Sun, L F, Liu, Z Q, Ma, V C, Tang, D S, Zhou, W Y, Zou, X P, Li, Y B, Lin, J Y, Tan, K L, Xie, S S (2001) “Growth of nanofibers array under magnetic force by chemical vapor deposition”, Chemical Physics Letters 336:392–396, discloses the growth of carbon nanofibres under magnetic force by means of a CVD process.
Zhu, H, Ci, L, Xu, C, Liang, J, Wu, D (2002) “Growth mechanism of Y-junction carbon nanotubes”, Diamond and Related Materials 11:1349–1352, discloses a growth mechanism of Y-junction carbon nanotubes.
Gan, B, Ahn, J, Zhang, Q, Rusli, Yoon, S F, Yu, J, Huang, Q F, Chew, K, Ligatchev, V A, Zhang, X B, Li, W Z (2001) “Y-junction carbon nanotubes grown by in situ evaporated copper catalyst”, Chemical Physics Letters 333:23–28, discloses Y-junction carbon nanotubes grown by means of an evaporated copper catalyst.